Physical factors such as stream flooding, streambed scour and fill, and fine sediment deposition can significantly impact the survival of salmon eggs and embryos (Lisle and Lewis 1992, DeVries 1997). This report aims to provide a description of the foundation for watershed restoration actions outlined in the Skagit Chinook Recovery Plan, specifically focusing on improving egg-to-fry survival for Chinook salmon.
The peak flow map for mountain basins illustrates estimated changes in peak flows within these basins. These alterations are attributed to variations in rain-on-snow runoff and the expansion of drainage networks due to the presence of roads (Figure 4). The ratings presented in the map are averaged by Watershed Assessment Units (WAU) and are based on available GIS data for roads and land cover. Since comprehensive flood history data for unregulated mountain sub-basins in the Skagit watershed is limited, the peak flow ratings were developed using an empirical correlation between land use and increased peak flows observed in the North Fork Stillaguamish River Basin, which has experienced a significant rise in peak flows.
The information and analysis presented in this report serve as a basis for implementing targeted measures aimed at restoring and enhancing the survival of Chinook salmon from the egg to fry stage in the Skagit watershed.
“Figure 4. Map of watersheds and Chinook salmon spawning ranges indicating the state of peak flow hydrology”.
In forested mountain basins, watersheds were classified as "peak flow impaired" when the 2-year flood magnitude under disturbed watershed conditions equaled or surpassed the 5-year flood magnitude under natural watershed conditions. Increased peak flow in these areas is commonly attributed to two factors: hydrologically immature vegetation and the drainage networks associated with forest roads, which exacerbate channel compaction and extension (Montgomery 1993, Washington Forest Practices Board 1995).
They attempted to apply this diagnostic using available data but encountered significant limitations (Table 1) in identifying changes in peak flow. Among the six monitored sites with long-term records, only three were unregulated basins unaffected by flood storage capability. None of these unregulated basins exhibited a statistically significant increasing trend in annual peak flow over their respective record periods, as determined by regression analysis (alpha level at 0.05).
Peak flows directly impact salmon eggs by mobilizing the streambed, potentially reaching the depth of the egg pocket and leading to the removal or crushing of the eggs (Holtby and Healey 1986, Montgomery et al. 1996, DeVries 1997). This phenomenon has been observed in Chinook salmon originating from the Skagit River by Seiler et al. (2002), who demonstrated a strong negative correlation between peak flows during the egg incubation period and the survival of Chinook salmon eggs to the fry stage.
“Figure 1. Relationship between peak Skagit River stream flow during egg incubation and egg-to-migrant-fry survival for Skagit River Chinook salmon (Data from Seiler et al. 2002)”.
When flood levels are below a 2-year event, the survival of eggs to the migrant fry stage shows some variability and generally remains high. This is likely because the energy during such floods is insufficient to mobilize the streambed significantly. However, for flood events larger than 2 years, there is a clear and consistent linear decrease in survival. This decrease is attributed to the increasing disturbance caused by higher flood energy, leading to greater impacts on the streambed.
The movement of streambed material during peak flows also indirectly affects the survival of eggs to the migrant fry stage. Bedload material movement can result in increased deposition of fine sediment, which infiltrates into and around the egg pocket. This reduces the permeability and pore size of the gravel, hindering water movement and reducing dissolved oxygen levels. The reduced oxygen levels can delay embryo development, lead to premature emergence before yolk sac absorption is complete, and result in smaller emergent fry. These effects collectively diminish the ability of fry to compete for resources and increase their vulnerability to predation, negatively impacting egg-to-fry survival.
It is evident that the magnitude of flood events plays a crucial role in determining the survival of Chinook salmon eggs until the fry stage. However, it's important to recognize that flood events are natural processes that also contribute to the formation and maintenance of vital rearing habitats that support salmon populations and productivity. Focusing solely on eliminating flood events would likely have adverse effects on the rearing stages of juvenile salmon. Therefore, rather than targeting floods for salmon recovery efforts, it is essential to assess and address any impairment of natural processes that may cause higher-than-normal flood magnitudes or frequencies.
Physical factors such as stream flooding, streambed scour and fill, and fine sediment deposition can significantly impact the survival of salmon eggs and embryos (Lisle and Lewis 1992, DeVries 1997). This report aims to provide a description of the foundation for watershed restoration actions outlined in the Skagit Chinook Recovery Plan, specifically focusing on improving egg-to-fry survival for Chinook salmon. The peak flow map for mountain basins illustrates estimated changes in peak flows within these basins. These alterations are attributed to variations in rain-on-snow runoff and the expansion of drainage networks due to the presence of roads (Figure 4). The ratings presented in the map are averaged by Watershed Assessment Units (WAU) and are based on available GIS data for roads and land cover. Since comprehensive flood history data for unregulated mountain sub-basins in the Skagit watershed is limited, the peak flow ratings were developed using an empirical correlation between land use and increased peak flows observed in the North Fork Stillaguamish River Basin, which has experienced a significant rise in peak flows. The information and analysis presented in this report serve as a basis for implementing targeted measures aimed at restoring and enhancing the survival of Chinook salmon from the egg to fry stage in the Skagit watershed.
“Figure 4. Map of watersheds and Chinook salmon spawning ranges indicating the state of peak flow hydrology”.
In forested mountain basins, watersheds were classified as "peak flow impaired" when the 2-year flood magnitude under disturbed watershed conditions equaled or surpassed the 5-year flood magnitude under natural watershed conditions. Increased peak flow in these areas is commonly attributed to two factors: hydrologically immature vegetation and the drainage networks associated with forest roads, which exacerbate channel compaction and extension (Montgomery 1993, Washington Forest Practices Board 1995). They attempted to apply this diagnostic using available data but encountered significant limitations (Table 1) in identifying changes in peak flow. Among the six monitored sites with long-term records, only three were unregulated basins unaffected by flood storage capability. None of these unregulated basins exhibited a statistically significant increasing trend in annual peak flow over their respective record periods, as determined by regression analysis (alpha level at 0.05). Peak flows directly impact salmon eggs by mobilizing the streambed, potentially reaching the depth of the egg pocket and leading to the removal or crushing of the eggs (Holtby and Healey 1986, Montgomery et al. 1996, DeVries 1997). This phenomenon has been observed in Chinook salmon originating from the Skagit River by Seiler et al. (2002), who demonstrated a strong negative correlation between peak flows during the egg incubation period and the survival of Chinook salmon eggs to the fry stage.
“Figure 1. Relationship between peak Skagit River stream flow during egg incubation and egg-to-migrant-fry survival for Skagit River Chinook salmon (Data from Seiler et al. 2002)”.
CODE: https://github.com/Salmon-Ecology-Library/Functional-Relationships/blob/main/code/Beamer_2005.R DATA: https://github.com/Salmon-Ecology-Library/Functional-Relationships/blob/main/data/Beamer_et_al_2005.csv PLOT: https://github.com/Salmon-Ecology-Library/Functional-Relationships/blob/main/plots/beamer_et_al_2005.png
When flood levels are below a 2-year event, the survival of eggs to the migrant fry stage shows some variability and generally remains high. This is likely because the energy during such floods is insufficient to mobilize the streambed significantly. However, for flood events larger than 2 years, there is a clear and consistent linear decrease in survival. This decrease is attributed to the increasing disturbance caused by higher flood energy, leading to greater impacts on the streambed. The movement of streambed material during peak flows also indirectly affects the survival of eggs to the migrant fry stage. Bedload material movement can result in increased deposition of fine sediment, which infiltrates into and around the egg pocket. This reduces the permeability and pore size of the gravel, hindering water movement and reducing dissolved oxygen levels. The reduced oxygen levels can delay embryo development, lead to premature emergence before yolk sac absorption is complete, and result in smaller emergent fry. These effects collectively diminish the ability of fry to compete for resources and increase their vulnerability to predation, negatively impacting egg-to-fry survival. It is evident that the magnitude of flood events plays a crucial role in determining the survival of Chinook salmon eggs until the fry stage. However, it's important to recognize that flood events are natural processes that also contribute to the formation and maintenance of vital rearing habitats that support salmon populations and productivity. Focusing solely on eliminating flood events would likely have adverse effects on the rearing stages of juvenile salmon. Therefore, rather than targeting floods for salmon recovery efforts, it is essential to assess and address any impairment of natural processes that may cause higher-than-normal flood magnitudes or frequencies.